This invention relates to the field of corneal esthesiometry. Corneal esthesiometry is concerned with the measuring of thresholds of the optic cornea to pressure stimuli. Specifically, this invention relates to the determination of thresholds for specific loci on the optic cornea. Other regions of the surface of the eye can be evaluated, as well.
This invention is related to previous procedures that have been used to measure corneal sensation. The two current popular methods employed to assess corneal thresholds use a solid probe to stimulate the cornea. A different recent method employs laser light that heats the cornea. Historically, air has been blown at the cornea to elicit reports of sensation or a blink reflex.
Concerning the two current popular methods, for each stimulation, the probe approaches the eye in view of the person being tested. The first popular known device, Millodot's Cochet-Bonnet esthesiometer, is a hand-held or a device-held variant of the von Frey esthesiometer. The Cochet-Bonnet esthesiometer is an esthesiometer which controls the stimulation force by means of varying the length of the probe, a wire. The wire is used to stimulate the cornea. Stimulation with the wire , however, has been shown to damage the cornea, and visible damage seen after testing with the Cochet-Bonnet apparatus is associated with an induced increase in threshold. See, for example, Millodot, M., & O'Leary, J. 1981: Corneal Fragility and Its Relationship to Sensitivity, Acta Ophthalmologica, 59, 820-826.
The second popular device, the Draeger corneal esthesiometer, is a more sophisticated mechanical device which thrusts or places a metal pin, the probe, against the cornea. The Draeger device cannot be used for people with normal corneal thresholds without causing pain. See, for example, Martin, X. Y., & Safran, A. B. 1988: Corneal hypoesthesia, Survey of Ophthalmology, 33, 28-40. Thus the Draeger device cannot measure thresholds in people with normal sensitivity.
With respect to the use of lasers, the current laser technique uses the tear-film of the eye to transduce laser energy into heat energy, which is then felt by the subject. The perceptual experience of the subject from heat production is nociceptive rather than due to a temperature gradient (i.e., heat or warmth). See, for example, Beuerman, R. W. & Tanelian, D. L. 1979: Corneal pain evoked by thermal stimulation, Pain, 7, 1-14.
In addition to these devices, devices made by others have used air to stimulate the cornea. See, for example, Goldberg et al., 1943; Morganroth & Richman, 1943; Jalavisto et al., 1951; and Boberg-Ans, 1956. The esthesiometer made by Jalavisto is representative of air-based (or gas-based) corneal esthesiometers. Jalavisto made an air-based corneal esthesiometer which stimulated the entire corneal surface at once. In these air-based devices, though, other nearby structures (body portions) were inadvertently stimulated (by air diffracting off the blocking edge of the rotating disk). For example, the eye lid, nose, or sclera was probably inadvertently stimulated. When nearby structures are inadvertently stimulated, the tester doesn't know if the resultant threshold is from the cornea or from some other structure. Boberg-Ans dismisses such esthesiometers, stating "It may thus be seen that the air-puff-technique contains so many problems and uncertainties that it cannot be employed for clinical scientific measurement of corneal study" (p. 161).
The entire contents of all of the references listed at the end of this specification are incorporated herein by reference.